Familiarization with voltage and current measurements. 1. Disconnect your training system from the wall outlet.

Transcription

1 Job Sheet 6 Geothermal Heat Pumps OBJECTIVE In this job sheet, you will determine the coefficient of performance (COP) and the energy efficiency ratio (EER) using measured temperature, humidity, voltage, and current values. PROCEDURE In this job sheet, you will measure voltage and current with the equipment running, if you are not familiar with taking these measurements or if you do not want to do them yourself, ask for assistance. Familiarization with voltage and current measurements In this part of the exercise, you will perform a simulation of the steps required to measure voltage and current in the heat pump disconnect switch. The simulation will allow you to familiarize yourself with the procedure with the power turned off. 1. Disconnect your training system from the wall outlet. 2. Put on isolating gloves. Be sure to wear these gloves when performing all the electric manipulations. 3. Open the disconnect switch box as shown in Figure 100. Figure 100. Open the disconnect switch. Festo Didactic

2 4. Remove the cover plate as shown in Figure 101. Figure 101. Remove the cover plate. 5. Insert a small screwdriver into the opening, as shown in Figure 102, to remove the nameplate. Insert a small flat screwdriver into the hole Figure 102. Remove the nameplate. 140 Festo Didactic

3 6. Encircle the black wire with the clamp meter, then the white wire, as shown in Figure 103 to measure the current flowing in each wire. A single wire should be inside the closed loop of the clamp meter, unless the sum of currents is required. The current is used to calculate the power consumed by the heat pump. For more details about current measurements, refer to Job Sheet 8. Figure 103. Current measurement. 7. Using a multimeter (or a voltmeter) place the probes on the screw terminals as shown in Figure 104. Later in the experiment, you will measure the voltage across these terminals to calculate the power consumed by the heat pump. For more details about voltage measurements, refer to Job Sheet 8. Figure 104. Voltage measurement. Festo Didactic

4 8. Repeat the simulation until you are familiar with the procedure to measure current and voltage. Be sure you are comfortable with each step in the process before you work with live lines. 9. Connect your training system to a wall outlet. 10. Perform the following settings on your training system: Main power switch... Off Thermostat... Cooling mode Temperature set point... 5 C (9 F) below room temperature Valve HV-1... Open Valve HV-2... Open Valve HV-3... Open Valve HV-4... Open Valve HV-5... Open Valve HV-6... Open Valve HV-7... Open Valve HV-8... Closed Valve HV-9... No adjustments required Valve HV Handle in horizontal position Valve HV Open Valve HV Open Valve HV Open Pressure gauge PI-1 selector switch... Right Pressure gauge PI-2 selector switch... Right Desuperheater On/Off switch... Off Priming tank three-way valves... Pumping station three-way valves... Air distribution register... Open 11. Set the main power switch to On. Make sure that the blower is running and the compressor indicator light is Off. Complete Table 22 by measuring the voltage and current consumed by the heat pump. This step gives you the opportunity to measure the blower current. Note that the current should be the same (up to a sign, as the sum of the two currents is zero) when measured from the black or white wire. Table 22. Blower voltage and current. Voltage (V) Current (A) 142 Festo Didactic

5 12. Once the compressor indicator light turns on wait ten minutes for the system to stabilize and complete Table 23. The current measured during this step corresponds to the sum of the blower and the compressor current. Table 23. Blower plus compressor voltage and current in cooling mode. Voltage (V) Current (A) 13. Using the clamp meter and the anemometer, complete Table 24. Wait for the humidity measurements to be stable. Table 24. Temperature and humidity in cooling mode. Temperature at the air intake ( ) Relative humidity at the air intake Temperature at the air distribution ( ) Relative humidity at the air distribution 14. Set the thermostat operating mode to Off. 15. Calculate the compressor electric work using Equation (6-3). (6-3) where is the compressor electric work in W is the measured voltage in V is the compressor current in A is the motor power factor (0.99) a The compressor current can be evaluated from the values in Table 22 and Table 23. Compressor electric work : Energy efficiency ratio in cooling mode 16. Assuming the system air flow is m 3 /s (500 ft 3 /m), use your results from Table 24 and a psychrometric chart (Figure 87 or Figure 88) to determine the energy efficiency ratio in cooling mode. Energy efficiency ratio in cooling mode: Festo Didactic

6 Coefficient of performance in heating mode The coefficient of performance (COP) is defined as the result of the refrigeration effect divided by the compressor electric work. In the following steps, you will calculate the COP using air temperatures and electric measurements. 17. Set your training system to the heating mode. Wait ten minutes after the compressor indicator light turns on before completing Table 25 by measuring the voltage and current consumed by the heat pump. Table 25. Blower plus compressor voltage and current in heating mode. Voltage (V) Current (A) 18. Take the measurements required to complete Table 26. Table 26. Temperature and humidity in heating mode. Temperature at the air intake ( ) Relative humidity at the air intake Temperature at the air distribution ( ) Relative humidity at the air distribution 19. Set the thermostat operating mode to Off. 20. Assuming the system air flow is m 3 /s (500 ft 3 /m), calculate the amount of heat gained by the air ( ). a Refer to Job Sheet 5 to calculate if necessary. Amount of heat gained by the air ( ): 21. Calculate the compressor electric work using Equation (6-4). (6-4) where is the compressor electric work in W is the measured voltage in V is the measured current in A is the motor power factor (0.99) Compressor electric work : 144 Festo Didactic

7 22. Calculate the coefficient of performance (COP) using the electric work ( ) from step 21, the amount of heat gained by the air ( ) from step 20 and Equation (6-5). (6-5) where COP is the coefficient of performance is the air heat gain is the compressor electric work Coefficient of performance (COP): 23. If you compare the method used to calculate the COP in Job Sheet 4 and the method used in this job sheet, which one do you think is easier to perform on the site of a project? 24. Set the main power switch to Off. Name: Date: Instructor's approval: Festo Didactic